Personal Narrative Of Travels To The Equinoctial Regions Of America During The Years 1799-1804 - Volume 1 - By Alexander Von Humboldt And Aime Bonpland.
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We
Struck Off With Difficulty Some Fine Specimens, Leaving Masses That
Were Eight Or Ten Inches Square Untouched.
I never saw in Europe
such fine hyalites as I found in the island of Graciosa, and on the
rock of porphyry called el Penol de los Banos, on the bank of the
lake of Mexico.
Two kinds of sand cover the shore; one is black and basaltic, the
other white and quartzose. In a place exposed to the rays of the
sun, the first raised the thermometer to 51.2 degrees (41 degrees
R.) and the second to 40 degrees (32 degrees R.) The temperature of
the air in the shade was 27.7 or 7.5 degrees higher than that of
the air over the sea. The quartzose sand contains fragments of
feldspar. It is thrown back by the water, and forms, in some sort,
on the surface of the rocks, small islets on which seaweed
vegetates. Fragments of granite have been observed at Teneriffe;
the island of Gomora, from the details furnished me by M.
Broussonnet, contains a nucleus of micaceous schist: - the quartz
disseminated in the sand, which we found on the shore of Graciosa,
is a different substance from the lavas and the trappean porphyries
so intimately connected with volcanic productions. From these facts
it seems to be evident that in the Canary Islands, as well as on
the Andes of Quito, in Auvergne, in Greece, and throughout the
greater part of the globe, subterraneous fires have pierced through
the rocks of primitive formation.
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